This application is related to Japanese Patent Application No. 2000-225418 filed in Jul. 26, 2000, whose priority is claimed under 35 USC xc2xa7119, the disclosure of which is incorporated by reference in its entirety.
1. Field of the Invention
The present invention relates to a light scanning apparatus and, more particularly, to a light scanning apparatus for use in an image forming apparatus, such as a laser printer or a digital copying machine, adapted to record an image on a scanning object by scanning a laser beam over the scanning object for light exposure according to image information.
2. Description of the Related Art
Overfilled-mode light scanning apparatuses are known in which a light beam (incoming beam) having a greater width than the width of each reflective facet of a multi-facet rotary mirror is reflected on the reflective facet and the reflected light beam (outgoing beam) is scanned over a scanning object (see, for example, Japanese Unexamined Patent Publications No. 11-218702 (1999) and No. 10-213767 (1998)). There are two types of overfilled-mode light scanning apparatuses: a center incidence type which is constructed so that the center axis of a scanning plane of the outgoing beam to be directed to the scanning object (scanning angle center axis) is coplanar with the center axis of the incoming beam in a plane extending through the rotation axis of the multi-facet rotary mirror (rotation axis plane) and the incoming beam and the outgoing beam are both allowed to pass through an fxcex8 lens; and an oblique incidence type which is constructed so that the center axis of the incoming beam and the scanning angle center axis of the outgoing beam are present in different rotation axis planes of the multi-facet rotary mirror and only the outgoing beam but not the incoming beam is allowed to pass through the fxcex8 lens.
The overfilled-mode light scanning apparatus of center incidence type has a light source and an incident optical system including an optical component for shaping the incoming beam into a rectangular cross section, a deflection mirror for deflecting the incoming beam before incidence on the fxcex8 lens, and the like. The incident optical system is disposed generally perpendicularly to tandem arrangement of the multi-facet rotary mirror and the fxcex8 lens, so that the light scanning apparatus has a great projection extending along the length of the incident optical system. This is disadvantageous in housing design with a lot of dead spaces in an apparatus housing, which may needlessly occupy a space in an image forming apparatus employing the light scanning apparatus. This results in the size increase of the light scanning apparatus and the image forming apparatus thereby to deteriorate the design flexibility thereof.
In the overfilled-mode light scanning apparatus of oblique incidence type, the incoming beam is deflected by a deflection mirror and directly incident on the multi-facet rotary mirror not via the fxcex8 lens. Therefore, an incident optical system is disposed as extending in an opposite direction from the traveling direction of the outgoing beam reflected on the multi-facet rotary mirror. Accordingly, the light scanning apparatus also has a partial projection with a dead space in an apparatus housing. This results in the size increase of the light scanning apparatus and an image forming apparatus employing the same, thereby deteriorating the design flexibility thereof.
In the overfilled-mode light scanning apparatus of oblique incidence type, the multi-facet rotary mirror has a smaller effective reflection width, so that the absolute light amount of a light spot to be scanned in a scanning direction across the scanning object is reduced, resulting in an extremely reduced beam utilization efficiency.
In view of the foregoing, the present invention is directed to a light scanning apparatus which provides a beam utilization efficiency close to that provided by the overfilled-mode light scanning apparatus of center incidence type and has a smaller size.
In accordance with the present invention, there is provided a light scanning apparatus which comprises: beam emitting means for emitting a light beam; a multi-facet rotary mirror having a plurality of reflective facets for reflecting the light beam emitted from the beam emitting means and rotatable for scanning the light beam reflected on the reflective facets over a scanning object; an incident optical system for shaping the light beam emitted from the beam emitting means to allow the light beam to have a greater width than the width of each of the reflective facets of the multi-facet rotary mirror as measured in a scanning direction for overfilled facet illumination and guiding the light beam to the multi-facet rotary mirror; and an fxcex8 lens provided in a path of the light beam extending from the multi-facet rotary mirror to the scanning object; wherein the incident optical system includes deflection means provided between the fxcex8 lens and the scanning object for deflecting the light beam emitted from the beam emitting means toward the multi-facet rotary mirror so as to cause the light beam deflected by the deflection means to pass through an end portion of the fxcex8 lens to reach the multi-facet rotary mirror.